Electronic message timing circuit



March 31, 1959 s. K. FERGUSON ELECTRONIC MESSAGE TIMING CIRCUIT INVENTOR.

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SYRL K. FERGUSON ATTORNEY United States Patent '0 1 2,880,320 ELECTRONIC MESSAGE TIMING CIRCUIT Syrl K. Ferguson, Springfield, Ya assignor to the United States of 'Anirica"as represented by the Secretary of the Army Original application April 23,1953, Serial No. 350,782,

now Patent No. 2,8 06,901, dated September 17,. 1957. lzigigsd-and" this application May 22,1957, Serial No. 6 1

1 Claim. (Cl. 250-27) (Granted under Title 35, U. S. Code (1952), sec. 26.6)

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This application is a division of my application, Serial No. 350,782, filed April 23, 1953, now Patent No. 2,806,901, granted September 17, 1957 under the same title.

This invention relates to a pulse generating system, and in particular to a pulse generating system particularly useful in apparatus for the transmission of messages over printing telegraph circuits and the like.

It is one object of this invention to provide a pulse timing circuit for use in printing telegraph systems.

It is a further object of this invention to provide a timing circuit which is particularly for use in printing telegraph systems utilizing the standard printing Baudot code.

In a preferred embodiment of this invention an oscillator is utilized as a timing element for the unit length pulse of the printing telegraph code. This oscillator runs at approximately 45 cycles per second at which frequency the period of one sine wave cycle equals 22 milliseconds. This period is used because the accepted standard rate of transmission is 60 words per minute and the average number of characters per word is considered to be five plus a space, thus requiring six characters to be transmitted each second. The time alloted to each character, therefore, is approximately 165 milliseconds. The Baudot code used herein utilizes six pulses of unit length and one pulse of one and one-half unit length to transmit each character; thus each pulse has a period of 22 milliseconds.

The first pulse of the Baudot code is the start pulse, the next five pulses carry the intelligence and the top pulse comprises a remaining period of approximately one and one-half time units. The standard printing telegraph or Baudot code presently consists of a marking stop pulse of 1.42 units or approximately 31 milliseconds duration. This stop pulse of 1.42 units is merely the minimum since during idle conditions the stop pulse could be extended indefinitely.

In view of the difificulties encountered in precise stopping and starting of an oscillator, it was decided to use a continuously running oscillator. It was also decided to use a stop pulse of 1.5 units duration because of the difliculty of acquiring a 1.42 pulse with a continuously running oscillator or multivibrator. There is no impairment of signal quality and the difference in duration of a character by only approximately 2 milliseconds is not apparent without precise measurement. Furthermore, the International Standard is to be a 7 /2 unit code. The invention may be better understood from a consideration of the following description of an embodiment thereof when read in conjunction with the accompanying drawings, in which Fig. l is a block diagram of the timing circuit according to this invention.

Fig. 2 is a diagram showing in schematic form a dual cathode follower circuit which may be used in the practice of this invention.

Referring-now to the drawings and particularly to Fig. 1 the oscillator 11 provides a sine wave output which is squared by the squaring amplifier 12 whose output is divided into two channels, one going directly to the dual cathode follower 14 and the other channel incorporating a phase inverter or delaying device 13 'for delaying the squared signal 180". The two squared signals are differentiated and applied to grids of the dual cathode follower stage by capacitors24 and 25 as shown in Fig.2. I The cathode followers 28 and 29 are biased tocut off by potentiometers 26 and 27 so that the negative pulses are discarded.

At the output 35 of the dual cathode follower stage, a train of pulses is provided and if both cathode followers were simultaneously operative, these pulses would be spaced apart 11 milliseconds. However, only one cathode follower has plate voltage applied at a time, therefore, the pulses are spaced at 22 millisecond intervals so long as relay 34 remains in one position. In such a case these pulses could be utilized to trigger each stage of an 8 stage distributor, as described in the parent application, at 22 millisecond time intervals and would require 176 milliseconds for each character transmitted; the stop pulse would consume two time units instead of the desired 1.5 time units. This would not comply with the standard rate of 60 words per minute as set forth above, and merely increasing the frequency would shorten the time space between pulses to less than the standard 22 millisecond interval.

Relay 34, of Fig. 2 is associated with flip flop circuit 18. In the parent application, S.N. 350,782, circuit 18 is also used to drive a character ring circuit. The function of relay 34 is to switch the plate voltage from one cathode follower stage to the other during the stop pulse period thereby reducing the time between two successive pulses in this one period to 11 milliseconds or 0.5 unit. The switching is accomplished by the action of armature 31 moving between relay contacts 30 and 32, as indicated in Fig. 2 of the drawings. This 11 millisecond pulse plus the first pulse in the next series added together give the 1.5 unit stop pulse. Since the next seven pulses are also spaced 22 milliseconds apart, the second group of pulses is effectively shifted along this time axis 11 milliseconds with respect to the first group of pulses as illustrated in Figure 1 along the output arrow from block 14.

It follows from the above discussion that there are provided by the time circuit two series of pulses, the individual pulses being spaced by 22 milliseconds, and a time interval between the series of pulses which is only one-half as great as the spacing between the individual pulses or 11 milliseconds. This cycle of operation continues so long as the equipment is being operated.

It is obvious that the principles of the present invention can be extended to provide a time interval between successive pulse trains that is a third of the time unit between successive pulses in the pulse train by using three channels feeding three output stages with the second and third channels having and 240 phase delay stages respectively. It follows then that the time interval between successive trains should be made any aliquot part of the time unit between successive pulses in the pulse trains by merely providing the appropriate number of output stages and a separate channel having the proper delay for each output stage.

The output stage does not necessarily need to be a cathode follower, any device which will provide the necessary signal strength and the proper output impedances could be used in this system.

What I claim is:

A pulse timing circuit for providing a time spacing between a first and second series of pulses of a predetermined repetition rate that is an aliquot part of the spacing between successive pulses of said series of pulses comprising: a source of square-wave signals, means for differentiating a first output signal from said source, a switching apparatus, means for applying said differentiated signal to said switching apparatus, means for delaying a second output signal from said source, means for differentiating said second signal and applying said second signal to said switching apparatus; said switching apparatus comprising, a pair of tubes connected in a dual cathode follower arrangement, a relay means for alternately applying an anode potential to the first and second of said tubes, a flip-flop circuit connected in circuit with said relay to operate the relay at a predetermined rate, a common cathode impedance for said pair of tubes, and output terminals across said impedance means, whereby said switching apparatus connects only said first signal to the output terminals during a first time period to transmit a first series of pulses, and connects only said second signal to the output terminals during a second time period.

iieferences Cited in the file of this patent UNITED STATES PATENTS 2,426,225 Krause Aug. 26, 1947 2,482,544 Jacobsen Sept. 20, 1949 2,482,759 Goodrich et al Sept. 27, 1949 

